Typically, semiconductor memory device, such as embedded non-volatile memory, includes a plurality of metal oxide semiconductor (MOS) units in a peripheral logic region thereof. These MOS units are used to achieve a data reading/writing circuit. To improve the performance of the MOS units, spacers are usually formed around gate structures thereof. However, in a typical process, spacers are also formed simultaneously around floating gates and control gates of the non-volatile memory device.
The inventors of the present disclosure found that the spacers consisting of materials such as silicon nitride indeed improve the performance of the date reading/writing circuit. However, some heating processes are necessarily required in semiconductor fabricating process, and after these heating processes, the silicon nitride spacers around the floating gates and the control gates may lead to the shifting of the threshold of the erasing voltage of the non-volatile memory device. As a result, the data retention of the non-volatile memory device significantly deteriorates. Therefore, there is a desire to achieve the improvement of the performance of the data reading/writing circuit while avoiding the significantly deterioration of the data retention.